The invention relates to a double-switching control valve for the injector of a fuel injection system for internal combustion engines, having a final control element actuated by an actuator, wherein the final control element and a bore of a housing form a radially defined annular chamber, which on its ends has a first recess and a second recess, and the final control element is axially displaceable by means of a tappet guided in a first guide bore and has both means for sealing off the annular chamber from the first recess and means for sealing of annular chamber from the second recess.
The object of the invention is to furnish a double switching control valve for an injector of a fuel injection system which allows the metering of the tiniest preinjection quantities and which is constructed simply and compactly.
This object is attained according to the invention by a control valve for the injector of a fuel injection system for internal combustion engines, having a final control element actuated by an actuator, wherein the final control element and a bore of a housing form a radially defined annular chamber, which on its ends has a first recess and a second recess, and the final control element is axially displaceable by means of a tappet guided in a first guide bore and has both means for sealing off the annular chamber from the first recess and means for sealing off the annular chamber from the second recess, and wherein the tappet is actuated by the actuator by means of a hydraulic booster.
The control valve of the invention has the advantage that the hydraulic booster shortens the switching times. The control pressure of the injector builds up an initial tension counter to the actuation direction of the actuator, so that the hydraulic booster does not become operative until it has built up a suitable counterpressure and is already in motion. Because of the very short switching times, very small preinjection quantities can also be metered. In addition, the control valve of the invention is simple in construction and consequently compact.
Variants of the invention provide that the first recess is in communication with a fuel return, and that the second recess is in communication with a control chamber, so that the demand for driving energy for the actuator is only slight, since only during the preinjection does the actuator have to perform work counter to the hydraulic forces acting on the final control element. Furthermore, the actuator is subject only to pressure stress, which is especially advantageous when piezoelectric actuators are used.
In a feature of the invention, the face end, remote from the final control element, of the tappet and a piston actuated by the actuator define a fluid-filled pressure chamber of the hydraulic booster, so that the travel or force boosting is effected simply and with little loss.
Another variant provides that a closing spring is present, which acts on the final control element counter to the actuation direction of the actuator, so that even if pressure is absent in the control chamber, the control valve always has a defined switching position, and the sealing action in the switching position between the main injection and the preinjection is improved.
Further in the invention, it is provided that the closing spring is disposed in the second recess and is braced against a shoulder in the housing and against the final control element, so that the engineering effort and expense are low. In a further embodiment, the closing spring is disposed in a third recess, which adjoins the control chamber, and is braced via a thrust rod, guided in a second guide bore, against the final control element and a Seeger ring that is disposed in an annular groove in the third recess, so that the second recess and the diameter of the second sealing seat can be kept small.
In a further variant, it is provided that the closing spring is disposed in a third recess, which adjoins the control chamber, and is braced via a thrust rod, guided in a second guide bore, against the final control element and a control piston protruding into the control chamber, so that a closing spring with a low spring rate and a small diameter can be used.
In a further embodiment, the thrust rod has at least one longitudinally extending groove, longitudinal bore, or flat face extending essentially over the length of the thrust rod, so that a hydraulic communication exists between the control chamber and the second recess. Furthermore, by suitable dimensioning of the groove, longitudinal bore or flat face, the function of the outlet throttle can be integrated into the thrust rod.
In one version of the invention it is provided that the final control element has a collar disposed coaxially to the longitudinal axis of the tappet, and that the means for sealing off the annular chamber from the second recess and/or the means for sealing off the annular chamber from the first recess have a frustoconical sealing cone disposed coaxially to the longitudinal axis of the tappet, so that over the entire service life of the control valve, good sealing action is achieved.
Further in the invention, the second sealing cone is part of a sleeve disposed coaxially to the longitudinal axis of the final control element, facilitating assembly, and the sleeve is also centered by the tappet.
A variant provides that the end face of the sleeve toward the final control element is smooth, and that the end face of the final control element toward the sleeve is smooth, so that the sleeve is centered not by the control piston but rather by the second sealing seat, and the sealing cone of the sleeve rests in the best possible way on the sealing face in the housing. The aforementioned smooth end faces furthermore seal off the annular chamber from the control chamber.
In a further feature of the invention, it is provided that the end face of the sleeve toward the final control element and the end face of the final control element toward the sleeve are frustoconical, so that the sleeve is centered by the tappet. Furthermore, the aforementioned end faces seal the annular chamber off from the control chamber.
In a further feature of the invention, the sleeve is separably joined to the final control element, so that assembly is simplified and there is no need to split the housing.
Another variant provides that the final control element is embodied spherically, and that the means for sealing off the annular chamber from the second recess and/or the means for sealing off the annular chamber from the first recess are sealing lines extending over the spherical surface, so that an especially compact, simple construction is achieved. Furthermore, the first guide bore and the first and second sealing seat need not be precisely aligned, since the spherical valve member centers itself.
In addition, between the bore and both of the first and second recesses, sealing faces are embodied, which cooperate with the means for sealing off the annular chamber from the first recess and/or the means for sealing off the annular chamber from the second recess, so that a still further improved sealing is achieved.
Further in the invention, it is provided that the housing is embodied in one piece, so that the number of sealing faces is reduced.
In one embodiment of the invention, the control valve is operated as a 2/3-way control valve, so that the metering of the tiniest preinjection quantities is improved, and at the same time large main injection quantities become possible.
In a variant of the invention, the actuator is a piezoelectric actuator, so that major forces and a rapid response are assured.
Further in the invention, it is provided that the injection system is a common rail injection system, so that the advantages of the control valve of the invention also benefit these injection systems.
The object stated above is also attained by an injector for a fuel injection system for internal combustion engines, having a control chamber controlled by a control valve, wherein the control valve has a final control element actuated by an actuator, wherein the final control element and a bore of a housing form a radially defined annular chamber, which on its ends has a first recess and a second recess, and the final control element is axially displaceable by means of a tappet guided in a first guide bore and has both means for sealing off the annular chamber from the first recess and means for sealing off the annular chamber from the second recess, and wherein the tappet is actuated by the actuator by means of a hydraulic booster.
The control valve of the invention has the advantage of shortened switching times. The control pressure of the injector builds up an initial tension counter to the actuation direction of the actuator, so that the hydraulic booster does not become operative until it has built up a suitable counterpressure and is already in motion. Because of the very short switching times, very small preinjection quantities can also be metered. In addition, the control valve of the invention is simple in construction and consequently compact.